Signals with nonsecure access include notably GPS signals of type C/A, L1C and L2C and Galileo signals of type L1C, E6C, E5a and E5b.
Signals with secure access include notably GPS signals P(Y) L1 and L2 and M and Galileo signals PRS L1 and E6.
Subsequently, the expressions secure GNSS signals and nonsecure GNSS signals will be used to denote GNSS signals with secure access and with nonsecure access, respectively.
The aim of the present invention is to simplify the use and to provide security for the performance of known GNSS systems, notably, but not only, for applications that involve the use of signals with secure access.
In order to perform a position calculation on the basis of secure GNSS signals, a classical receiver must implement a certain number of complex, notably cryptographic, processing operations that substantially increase their complexity and their cost.
Complexity is increased again when it is desirable to improve the precision of the navigation calculations performed, to implement an integrity check (authentication) on the received signals or to detect any spoofing.
In known radio navigation systems, the improvement in the vulnerability of GNSS applications is essentially provided by the final user, by introducing complex processing operations into the receivers that allow any decoys to be detected and an integrity check to be performed that allows the origin of the signals to be ascertained.
These additional processing operations, within the limits of present technology, notably increase the complexity and cost of the receivers, thus running counter to the possibilities of miniaturization and consumption reduction that are universally in demand.
The system proposed according to the invention allows a global improvement in the robustness and integrity of GNSS signals by using, for all of the GNSS receivers in a given geographical area, shared signal acquisition and tracking means, relocated to reference stations that provide reinforced capabilities for protecting the processing operations and for correcting the measurements.
The use of reference stations allows complex remote processing operations to be performed to the benefit of users and reduction of measurement errors linked to the propagation of the radio navigation signals (ionospheric and tropospheric errors) and to the environment close to the receiver (multipaths).
Moreover, the proposed solution notably improves the availability and integrity of positioning that is offered by satellite navigation systems.